Filter device

ABSTRACT

The invention relates to a filter device provided with at least one filter unit ( 10 ), which can be connected to a hydraulic circuit ( 14 ), with at least one supply ( 18 ) and one discharge line ( 18 ), and with at least one cooling unit ( 22 ). Said cooling unit is connected to a secondary branch line ( 20 ), is connected to the hydraulic unit ( 14 ) in a manner that is parallel to the supply line ( 18 ), and is supplied with a hydraulic medium by means of a switching device ( 24 ) once a predetermined temperature threshold value of the hydraulic medium to be cooled is attained. By virtue of the fact that a permanent supply ( 36 ) for the cooling unit ( 22 ) is provided in the direction of flow of the hydraulic medium in the supply line ( 18 ) before the switching device ( 24 ), and that this permanent supply ( 36 ), which is connected in parallel to the switching device ( 24 ), flows into the secondary branch line ( 20 ), it is possible to control the volume flow in reverse flow according to the fluid temperature, whereby a partial flow of the hydraulic medium in the supply line directly reaches the cooling unit also at low or reduced temperatures, at which the switching device has not yet been actuated, thereby ensuring that the cooling unit is permanently supplied with the hydraulic medium.

[0001] The invention relates to a filter device with the features of the preamble of claim 1.

[0002] In known approaches, as are freely available on the market, these filter devices are used in all types of hydraulic systems, especially also in construction machines. Filter units are among others so-called return line intake filters in which in a supply line the return lines of the respective hydraulic system discharge, the return lines being combined into so-called collectors which then ensure central inflow of the fouled fluid or hydraulic medium to the respective return line intake filter unit and after filtration the cleaned fluid being relayed to an intake connection which in turn supplies the hydraulic system with the cleaned hydraulic medium.

[0003] Furthermore it can be provided that in order to prevent overheating of the hydraulic system, a cooling unit be connected upstream to the supply line into which the return lines discharge before admission into the actual filter circuit in the secondary branch line, and a conventional thermostat controller can turn on or off the cooling unit depending on the operating temperature of the hydraulic medium. Especially at low temperatures of the hydraulic medium can the changeover means with the thermostat controller and/or the components of the cooling circuit itself produce a banking-up pressure which leads to pressure peaks in the upstream units, for example in a hydraulic motor and a hydraulic pump; this can damage their sealing elements. Furthermore the indicated fluid-carrying components in the known approach are connected to one another by way of the indicated collectors and lines, and producing the pertinent fluid-carrying connections can take place by way of conventional tubing technology using weld connections. Therefore the known filter devices are structurally large and expensive to produce.

[0004] DE-A-34 02 884 A1 discloses a filter device, a thermostat being installed in the system of regulating the temperature of the working liquid and opening or closing automatically the branch to the cooler depending on the temperature of the reversible working liquid in the system. The heated reversible working liquid flows directly out of the thermostat upstream of the filter into the intake branch of the filling liquid pump, i.e. bypassing the cooler and the tank. The thermostat therefore closes the throughflow of working liquid into the part of the circuit which contains the cooler and tank in the case in which the temperature of the working liquid is low. When the temperature of the working liquid reaches the value at which the thermostat opens, part of the working liquid flows through the connecting branch into the cooler and on into the tank. The thermostat opens entirely when the temperature of the working liquid in the tank reaches the optimum value. All the working liquid which returns from the closed hydraulic circuit continues to flow only by way of the cooler into the tank. In this known approach the thermostat can produce a banking-up pressure which leads to damaging pressure peaks in the upstream units especially at low temperatures of the hydraulic medium within the hydraulic circuit.

[0005] U.S. Pat. No. 3,990,424 discloses a generic filter device with at least one filter unit which can be connected to a hydraulic circuit, with at least one supply and drain line and with at least one cooling unit which is connected in the secondary branch line and which is connected parallel to the supply line into the hydraulic circuit, and by a changeover means at a definable temperature threshold value of the hydraulic medium which is to be cooled is supplied with the latter, in the flow direction of the hydraulic medium in the supply line upstream of the changeover means there being a permanent supply for the cooling unit and this permanent supply connected parallel to the changeover means discharging into the secondary supply line. In this known filter device which is used especially in jet-propelled racing boats, permanent supply is induced by way of the valve chamber to which the cooling unit is permanently connected to carry fluid, and depending on the respective temperature threshold value and therefore depending on the position of the changeover means, at low temperatures of the hydraulic medium the latter is supplied directly to the filter unit and at high temperatures of the hydraulic medium a detour takes place by way of the cooling unit before the medium which has then been cooled is supplied to the filter unit. As a result of the direct connection of the cooling unit to the valve chamber, in the system a damaging banking-up pressure can build up which leads to pressure peaks in the upstream units and in the cooling unit itself. In addition the cooling unit can be exactly matched as a function block to the intended valve chamber using connection technology; this allows production of the known design to become expensive.

[0006] Based on this prior art, the object of the invention is to further improve the known filter devices such that the damaging banking-up pressure in the system is avoided and still reliable operation is achieved. In addition it is to be guaranteed that the filter device has a small structure and is economical both in production and also in later operation. The pertinent object is achieved by the filter device with the features of claim 1.

[0007] With the embodiment of the features of the characterizing part of claim 1, it is possible to control the volumetric flow in the return line depending on the fluid temperature such that even at low temperatures at which the changeover device has not yet been actuated, a partial flow of the hydraulic medium in the supply line travels directly to the cooling unit so that the cooling unit is permanently supplied with the hydraulic medium. Due to the pertinent bypass circuit the banking-up pressure is on the cooling unit independently of the actuation situation of the changeover device, by which the cooling unit can be vented at any time if necessary.

[0008] The permanent supply can be easily combined structurally with the changeover means especially in one component so that in this way little construction space is required and the filter device as claimed in the invention can be accordingly produced and operated easily and economically.

[0009] In one preferred embodiment of the filter device as claimed in the invention the changeover device has an oil temperature controller which has an operating characteristic such that at low temperatures of the hydraulic medium it clears a path for it to the filter unit and when the temperature threshold is reached supplies the heated hydraulic medium to the cooling unit which relays the cooled fluid to the filter unit by way of the secondary branch line. In this way the cooling unit can be triggered with a high degree of precision for a cooling process which runs in a defined manner by means of the oil temperature controller. The oil temperature controller can be a commercial component known for example from the cooling circuit of internal combustion engines.

[0010] In another especially preferred embodiment of the filter device as claimed in the invention the permanent supply is provided with a choke such that especially in the operating situation “low temperature” for the hydraulic medium the banking-up pressure in the supply line is reduced. Furthermore, by way of the indicated choke venting of the downstream cooling unit is possible in any operating situation of the filter device. In the known filter devices the indicated venting is often only possible in the “high temperature” operating position or in a type of emergency operating position which however is to some extent only optionally available in the known devices.

[0011] In another preferred embodiment of the filter device as claimed in the invention, viewed in the flow direction of the hydraulic medium, upstream of the changeover device the return lines of a hydraulic motor and a hydraulic pump which in particular are combined into a hydrostatic transmission, discharge into the supply line, in the flow direction of the hydraulic medium downstream of the changeover device the return line of the working hydraulics likewise discharging into the supply line. In this way a compact structure for the filter device can be achieved and the conventional connecting lines and collector means which are to be welded together can be omitted. Therefore all connection possibilities for all existing modules are present combined into one unit; this leads to a filter device with a small structure. Preferably at least the changeover device and the permanent supply are a component of a filter head which can be connected to a housing part which holds the filter unit. In this way the filter device can be included in the common filter housing of the filter unit and trigger unit.

[0012] Other advantageous embodiments of the filter device as claimed in the invention are the subject matter of the other dependent claims.

[0013] The filter device as claimed in the invention is detailed below using one embodiment as shown in the drawings. The drawings are schematic and not to scale.

[0014]FIG. 1 shows a diagram for a known filter device as is freely available on the market;

[0015]FIG. 2 shows a diagram of the filter device as claimed in the invention with its essential components;

[0016]FIG. 3 shows in a perspective the filter device with its connections;

[0017]FIG. 4 shows in an overhead view a section through the filter housing which is shown in FIG. 3 with the cooling unit connected;

[0018]FIG. 5 and 6 show the respective position of the oil temperature controller at a low or high temperature.

[0019] In the known filter device as shown in FIG. 1 it is provided with a filter unit 10 of conventional design. The filter unit 10 is a component of a return line intake filter labelled 12 overall; its important components are encircled in FIG. 1 with a broken-line frame. The return line intake filter 12 is furthermore provided with a fouling display VA which delivers an optical or other signal indication with respect to the state of fouling of the actual filter unit 10. A spring-loaded check valve V2 in the manner of a bypass valve is connected to the bypass line to the filter unit 10. If the filter unit 10 is clogged by fouling, the pretensioned bypass valve 12 opens to the tank T and in this way dangerous pressure peaks cannot build up in the system. In the flow direction downstream of the filter unit 10 is the intake connection B which in conjunction with the spring-loaded check valve V1 produces a pretensioning pressure which ensures that the oil column in the hydraulic circuit 14 cannot separate. The possible closing pressure of the bypass valve V2 is chosen to be greater than that of the check valve V1 to prevent the fluid which is be filtered and which is supplied by way of the connection A from being drained unintentionally in the direction of the tank unfiltered into the latter with bypassing of the filter unit 10.

[0020] The hydraulic circuit 14 has a supply line 16 and a drain line 18, the latter being connected to the connection A of the return line intake filter 12. The cooling unit 22 is connected in the secondary branch line 20 which is connected parallel to the supply line 16 to the hydraulic circuit 14. Viewed in the direction of looking at FIG. 1 the secondary branch line 24 with its one free end discharges into the changeover means 24 and with its other free end into a collector 26 into which otherwise the supply line 16 discharges, as well as the drain line 18. At a definable temperature threshold value of the hydraulic medium to be cooled the changeover means 24 is actuated and supplies the hydraulic medium which is to be cooled to the cooling unit 22, then the cooled hydraulic medium being relayed by way of the secondary branch line 20 to the collector 26 and from there traveling by way of the drain line 18 into the return line intake filter 12.

[0021] After cleaning the fouled medium by way of the filter unit 10 then the fluid or hydraulic medium which has been cleaned in this way is returned by way of the intake connection B to the hydraulic circuit 14 to which for example a hydraulic pump of a machine or machine tool is connected. Next to the collector 26 there is another collector 28 into which the return line 30 of the hydraulic motor (not shown) and the return line 32 of a hydraulic pump (not shown) discharge. The hydraulic motor which is not detailed and the hydraulic pump which is not detailed are a component of a hydrostatic transmission which is not detailed and for which the illustrated filter device is used. Since the arrangements in this regard, especially the hydrostatic transmission, are prior art, they are not detailed here. Moreover the return line 34 of the actual working hydraulics (not shown) which has for example a conventional working cylinder for an excavator or the like discharges into the collector 26.

[0022] Especially at low temperatures for the hydraulic medium which arise for example when the hydraulic system is started up after having been idle for a long time, the components, especially also in the form of a return line intake filter 12, in the supply line 16 produce a resistance in the form of an increased banking-up pressure; in upstream units in the form of a hydraulic motor and hydraulic pump this can lead to damage of their sealing elements; this allows failure of the entire hydraulic system. To prevent this, in the embodiment of the filter device as claimed in the invention shown in FIG. 2 it is provided that in the flow direction of the hydraulic medium in the supply line 16 upstream of the changeover means 24 and independently of its position there is a permanent supply 36 for the cooling unit 22, this permanent supply 36 connected parallel to the changeover means 24 discharging into the secondary branch line 20 with the cooling unit 22. The permanent supply 36 is made essentially in the manner of another inflow line or inflow channel.

[0023] The components according to the filter device as claimed in the invention as shown in FIG. 2 are, to the extent they correspond to the known filter device shown in FIG. 1, labelled with the same reference numbers, the statements above in this regard also applying to the approach as claimed in the invention as shown in FIG. 2. Another difference is that the known collectors 26 and 28 in the approach as claimed in the invention have been completely omitted; rather a direct connection technique of the components among one another with their supply lines was achieved; this will be detailed below.

[0024] The approach as claimed in the invention also uses as the changeover means 24 a conventional oil temperature controller as is known for example in heating engineering. It has an operating characteristic such that at low temperatures of the hydraulic medium it clears the path for it to the filter unit 10 of the return line intake filter 12 and when the temperature threshold is reached supplies the heated hydraulic medium to the cooling unit 22 which relays the cooled fluid to the filter unit 10 by way of the secondary branch line 20. The permanent supply 36 in the form of a corresponding connecting line or a connecting channel is provided with a choke or a diaphragm such that especially in the operating situation “low temperature” for the hydraulic medium likewise a damaging banking-up pressure in the supply line 16 is avoided. Independently of the choke 38 in any case the line cross sections relative to the permanent supply 36 and the secondary branch line 20 are increased such that resistances in the hydraulic circuit 14 cannot occur in a relevant manner such that the banking-up pressure in the return lines 30, 32 is significantly increased. The permanent supply 36 in this regard with the choke 38 also allows venting relative to the cooling unit 22 in any operating situation of the filter device. There can also be a venting capability which can be actuated by hand directly on the changeover means 24.

[0025] As is shown in FIG. 3, in the preferred embodiment of the filter device as claimed in the invention all its components are combined into one unit. Thus at least the changeover means 24 and the permanent supply 36 are components of a termination or head part 40 which is made flange-like and which can be joined to the pot-like lower housing part 42 which holds the filter unit 10. In the area of the upper cover part 40 there are also connection possibilities for the working hydraulics A, the intake connection B and for the hydraulic motor or the hydraulic pump with respect to their return lines 30 and 32. In addition to these connecting points there are essentially in one plane the connecting points 44 and 46 for the connection of the secondary branch line 20 leading to the cooling unit 22 or originating from the cooling unit 22. There is furthermore the tank connection T on the bottom of the pot-like housing part 42.

[0026]FIG. 4 ff. impart an improved idea about the structure and operation of the changeover means 24 in conjunction with the structure and the action of the permanent supply 36. Thus the changeover means 24 in the form of the oil temperature controller has an expansion element 50 on which an energy storage device in the form of a compression spring 48 acts. Expansion elements 50 in this respect are relatively well known from motor vehicle engineering. The expansion element 50 triggers a sleeve-shaped pilot valve 52 which is guided in the valve space 54 to move lengthwise against the action of the compression spring 48. As FIG. 4 furthermore shows, the return lines 30 and 32 from the hydraulic motor and hydraulic pump discharge into the valve space 54. Furthermore, the supply line 16 which leads to the filter unit 10 and which passes at least partially as part of the valve space 54 into it discharges into the valve space 54.

[0027] In order to increase the free cross sectional area of the drain line 18. it is divided into two component branches 18 a,b, viewed in the direction of looking at FIG. 4 the actuating sleeve 52 in the controller position “low temperature” for the hydraulic medium covering the upper drain line branch 18 a except for a fluid-carrying passage 56 which viewed in the lengthwise direction of the actuating sleeve 52 passes through its wall part 58 in the middle and produces the fluid-carrying connection between this branch 18 a and the interior of the valve space 54. The secondary branch of the drain line 18 b, which branch is the bottom one viewed in the direction of looking at FIG. 4, is conversely kept entirely free from the wall part 58 of the pilot valve 52 and the lower boundary of the wall part 58 ends above the lower drain line 18 b. Between the two branches a,b of the drain line 18, viewed in the direction of looking at FIG. 4 from the right side, the connecting point 44 which leads by way of the secondary branch line 20 to the cooling unit 22, meshes with the valve space 54, in the controller position “low temperature” the pertinent connecting point being closed by the wall part 58 of the pilot valve 52, except for the choke 38 of the permanent supply 36 which establishes a permanent fluid-carrying connection between the connecting point 44 and the supply line 16. The indicated choke 38 is formed by a fluid-carrying passage between the annulus as part of the valve housing, discharges into the connecting point 44 on one side and the outside of the annular wall part 58 on the other side. The connecting point 46 to which part of the secondary branch line 20 is connected and which originates from the cooling unit 22 discharges directly into the fluid-carrying filter space of the filter unit 10. Furthermore, the lengthwise alignment of the valve space 54 runs crosswise to the lengthwise axis of the housing part 42 with the filter unit 10. The possible direction of flow through the cooling unit 22 by way of the secondary branch line 20 is shown in FIGS. 1, 2 and 4 with arrows.

[0028] The controller positions are detailed below using FIGS. 5 and 6. FIGS. 5 and 6 are shown in the viewing direction running 90° to the view as shown in FIG. 4. In the controller position “low temperature” the expansion element 50 in its retracted position and the compression spring 48 hold the sleeve-shaped pilot valve 52 in its end position which is the right position viewed in the direction of looking at FIG. 5 and in which the top of the pilot valve 52 adjoins the right boundary wall of the valve space 54. FIG. 5 corresponds therefore in terms of the position of the controller to FIG. 4. In the position in this respect the cold hydraulic medium which is supplied by way of the inflow lines 16, 30 and 32 to the valve space 54 is relayed by way of the valve space 54 or the passage 56 directly to the drain line 18 with its branches 18 a, 18 b so that the cold hydraulic medium can be supplied directly to the filter space with the filter unit 10, bypassing the cooling unit 22. But the cooling unit 22 is supplied permanently by way of the choke 38 with hydraulic medium of low temperature. Accordingly a damaging banking-up pressure in the return lines 30 and 32 cannot occur.

[0029] For the controller position “high temperature”, as shown in FIG. 6, the expansion element 50 is extended and the sleeve-shaped pilot valve 52 assumes it left-most position against the force of the compression spring 48 viewed in the direction of looking at FIG. 6, in which position the free bottom edge of the pilot valve 52 adjoins the left boundary wall of the valve space 54 as the stop part. The middle passage point 56 in the wall part 58 is then at the same height as the annular channel of the connecting point 44 which forms the choke 48 and the hydraulic medium which is to be cooled travels solely by way of the connecting point 44 and the secondary branch line 20 to the cooling unit 22. After passing through the cooling unit 22 then the cooled hydraulic medium travels by way of the connecting point 46 into the filter space with the filter unit 10. The remaining drain line 18 with its branches a, b is then closed essentially fluid-tight by way of the wall part 58 of the pilot valve 52. Therefore in the controller position “high temperature” hot hydraulic medium does not travel directly by way of the drain line 18 to the filter unit 10. With respect to the passage point 56 which is made large in cross section, in the controller position “high temperature” essentially hot hydraulic medium no longer flows through the choke 38, but the choke function is essentially canceled by clearing its choked cross section and drainage proceeds on a priority basis by way of the passage 56 in the wall part 58 of the pilot valve 52.

[0030] Because in the flow direction of the hydraulic medium in the supply line upstream of the changeover means there is an overflow channel 18 b parallel to the main channel 18 a and this channel enlarges the flow cross section at low temperatures, a damaging banking-up pressure regardless of the actuation situation of the changeover means is avoided. This overflow channel can be easily integrated structurally in the filter head, especially by combining the components of the filter and of the changeover means. Thus, in this respect less installation space is required and the filter device as claimed in the invention can accordingly be produced easily and economically using casting technology as well as easily and economically operated.

[0031] In the embodiment of a filter device as claimed in the invention shown in FIG. 2 it is therefore provided that two channels 18 a and 18 b as shown in FIG. 4 be attached in the drain line 18 and lead to the filter unit 10 which reduces the hydraulic resistance for the operating state “low temperatures”. 

1. A filter device with at least one filter unit (10) which can be connected to a hydraulic circuit (14), with at least one supply (16) and one drain (18) line and with at least one cooling unit (22) which is connected in a secondary branch line (20) and which is connected parallel to the supply line (16) into the hydraulic circuit (14) and at a definable temperature threshold of the hydraulic medium which is to be cooled is supplied with the latter by a changeover means (24), in the flow direction of the hydraulic medium in the supply line (16) upstream of the changeover means (24) there being a permanent supply (36) for the cooling unit (22) and this permanent supply (36) connected parallel to the changeover means (24) discharging into the secondary branch line (20), characterized in that the permanent supply (36) is made essentially in the manner of another inflow line or an inflow channel.
 2. The filter device as claimed in claim 1, wherein the changeover device (24) has an oil temperature controller which has an operating characteristic such that at low temperatures of the hydraulic medium it clears a path for it to the filter unit (10) and when the temperature threshold is reached supplies the heated hydraulic medium to the cooling unit (22) which relays the cooled fluid to the filter unit (100 by way of the secondary branch line (20).
 3. The filter device as claimed in claim 1 or 2, wherein the permanent supply (36) is provided with a choke such that especially in the operating situation “low temperature” venting of the cooling unit (22) is possible without emergency manual actuation.
 4. The filter device as claimed in one of claims 1 to 3, wherein in the supply line (16) in the flow direction of the hydraulic medium, upstream of the changeover device (24) the return lines (30, 32) of a hydraulic motor and a hydraulic transmission which are especially combined into a hydrostatic transmission discharge into the supply line, and wherein in the flow direction of the hydraulic medium downstream of the changeover device (24) the return line (34) of the working hydraulics likewise discharges into the supply line.
 5. The filter device as claimed in claim 4, wherein in the flow direction of the hydraulic medium an intake connection (B) is connected to the hydraulic circuit (14) downstream of the filter unit (10) and undergoes hydraulic pretensioning by way of a back pressure valve (V1), preferably in the form of a check valve.
 6. The filter device as claimed in one of claims 1 to 5, wherein at least the changeover means (24) and the permanent supply (36) are components of a head part (40) which can be joined to the housing part (42) which holds the filter unit (10).
 7. The filter device as claimed in claim 6, wherein the oil temperature controller has an expansion element (50) on which an energy storage device acts and which triggers a sleeve-shaped pilot valve (52) which is guided in the valve space (54) to be able to move lengthwise against the action of the energy storage device.
 8. The filter device as claimed in claim 7, wherein the return lines (30, 32) from the hydraulic motor and hydraulic pump discharge into the valve space (54), as does the supply line 16 which leads to the filter unit (10) including part of the secondary branch line (20) which leads to the cooling unit (22), and wherein the sleeve-shaped pilot valve (52) has a fluid-carrying passage (56) in its wall part (58).
 9. The filter device as claimed in claim 8, wherein the outside periphery of the wall part (58) with the assignable wall parts of the cover part (40) in which the pilot valve (52) is guided, in each position thereof borders the choke (38).
 10. The filter device as claimed in claim 1, wherein the drain line (18) consists of two channels (18 a and b) which avoid a damaging banking-up pressure. 